MMUSIC A. Begen Internet-Draft Y. Cai Intended status: Standards Track H. Ou Expires: September 13, 2011 Cisco March 12, 2011 Temporal Interleaving Attribute in the Session Description Protocol draft-begen-mmusic-temporal-interleaving-01 Abstract A straightforward approach to provide protection against network outages (or packet losses) with a longest duration of T time units is to simply duplicate the original packets and send each copy separated in time by at least T time units. This approach is commonly referred to as Temporal Redundancy or Temporal Interleaving. This document defines an attribute to indicate the presence of temporally redundant media streams and the interleaving period in the Session Description Protocol. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 13, 2011. Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Begen, et al. Expires September 13, 2011 [Page 1] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4 3. The 'interleaving-period' Attribute . . . . . . . . . . . . . . 4 4. SDP Examples . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Performance Evaluation and Reporting . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7.1. Registration of SDP Attributes . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . 6 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Begen, et al. Expires September 13, 2011 [Page 2] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 1. Introduction Consider that a media sender transmits an original source packet and transmits its duplicate after an interleaving period following the original transmission. If a network outage hits the original transmission, the expectation is that the second transmission arrives at the receiver. Alternatively, the second transmission may be hit by an outage or gets dropped, and the original transmission completes successfully. On the receiver side, both transmissions can also arrive and in that case, the receiver (or the node that does the duplicate suppression) needs to identify the duplicate packet(s) and discard them appropriately, producing a duplication-free stream. Temporal interleaving can be used in a variety of multimedia applications where there is sufficient bandwidth for the duplicated traffic and the application can tolerate the delay caused by interleaving. One particular use case is to improve the reliability of real-time video feeds inside a core IP network [IC2011]. Compared to other popular redundancy approaches such as Forward Error Correction (FEC) [I-D.ietf-fecframe-framework] and redundant data encoding (e.g., [RFC2198]), temporal interleaving is quite easy to implement since it does not require any special type of encoding or decoding. For duplicate suppression, the receiver has to be able to identify the identical packets. This is straightforward for media packets that carry one or more unique identifiers such as the sequence number field in RTP header [RFC3550]. The receiver can also use alternative approaches to compare the incoming packets and discard the duplicate ones. In this specification, we are not concerned about how the sender should determine the interleaving period or how the receiver can suppress the duplicate packets. Rather, we introduce a new attribute for the Session Description Protocol (SDP) [RFC4566] that indicates that the media stream is to be sent two or more times using the interleaving approach and also indicates the interleaving period for each additional duplication. In practice, more than two redundant streams for temporal interleaving are unlikely to be used since the additional delay and increased overhead are not easily justified. However, we define the new attribute in a general way so that it could be used with more than two redundant streams if needed. The new attribute is applicable to both RTP and non-RTP streams. Begen, et al. Expires September 13, 2011 [Page 3] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 2. Requirements Notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. The 'interleaving-period' Attribute The following ABNF [RFC5234] syntax formally describes the 'interleaving-period' attribute: interleaving-attribute = "a=interleaving-period:" periods CRLF periods = period *( ":" period) period = 1*DIGIT ; in milliseconds Figure 1: ABNF syntax for the 'interleaving-period' attribute The 'interleaving-period' attribute is defined as both a media-level and session-level attribute. It specifies the interleaving duration in milliseconds (ms). 4. SDP Examples In the example below, the multicast stream is duplicated with an interleaving period of 100 ms. v=0 o=ali 1122334455 1122334466 IN IP4 red.example.com s=Temporal Interleaving t=0 0 m=video 30000 RTP/AVP 100 c=IN IP4 233.252.0.1/127 a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1 a=rtpmap:100 MP2T/90000 a=interleaving-period:100 a=mid:S1 In the second example below, the multicast stream is duplicated twice. 50 ms after the original transmission, the first duplicate is transmitted and 100 ms after that, the second duplicate is transmitted. In other words, the same packet is transmitted three times over a period of 150 ms. Begen, et al. Expires September 13, 2011 [Page 4] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 v=0 o=ali 1122334455 1122334466 IN IP4 red.example.com s=Temporal Interleaving t=0 0 m=video 30000 RTP/AVP 100 c=IN IP4 233.252.0.1/127 a=source-filter:incl IN IP4 233.252.0.1 198.51.100.1 a=rtpmap:100 MP2T/90000 a=interleaving-period:50:100 a=mid:S2 5. Performance Evaluation and Reporting Editor's note: This section should discuss how the receiver should prepare the RTCP receiver reports or whether a new XR report is needed. 6. Security Considerations The 'interleaving-period' attribute is not believed to introduce any significant security risk to multimedia applications. A malevolent third party could use this attribute to misguide the receiver(s) about the interleaving periods and/or the number of redundant streams. For example, if the malevolent third party increases the value of the interleaving period, the receiver(s) will unnecessarily incur a longer delay since they will have to wait for the entire interleaving period. Or, if the interleaving period is reduced by the malevolent third party, the receiver(s) might not wait long enough for the duplicated transmission and incur unnecessary packet losses. However, these require intercepting and rewriting the packets carrying the SDP description; and if an interceptor can do that, many more attacks are also possible. In order to avoid attacks of this sort, the SDP description needs to be integrity protected and provided with source authentication. This can, for example, be achieved on an end-to-end basis using S/MIME [RFC5652] [RFC5751] when SDP is used in a signaling packet using MIME types (application/sdp). Alternatively, HTTPS [RFC2818] or the authentication method in the Session Announcement Protocol (SAP) [RFC2974] could be used as well. 7. IANA Considerations The following contact information shall be used for all registrations in this document: Begen, et al. Expires September 13, 2011 [Page 5] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 Ali Begen abegen@cisco.com Note to the RFC Editor: In the following, replace "XXXX" with the number of this document prior to publication as an RFC. 7.1. Registration of SDP Attributes This document registers a new attribute name in SDP. SDP Attribute ("att-field"): Attribute name: interleaving-period Long form: Interleaving period for temporally redundant streams Type of name: att-field Type of attribute: Media or session level Subject to charset: No Purpose: Specifies the interleaving period(s) for redundant stream(s) Reference: [RFCXXXX] Values: See [RFCXXXX] 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 8.2. Informative References [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [I-D.ietf-fecframe-framework] Watson, M., Begen, A., and V. Roca, "Forward Error Correction (FEC) Framework", draft-ietf-fecframe-framework-14 (work in progress), Begen, et al. Expires September 13, 2011 [Page 6] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 March 2011. [RFC2198] Perkins, C., Kouvelas, I., Hodson, O., Hardman, V., Handley, M., Bolot, J., Vega-Garcia, A., and S. Fosse- Parisis, "RTP Payload for Redundant Audio Data", RFC 2198, September 1997. [IC2011] Evans, J., Begen, A., Greengrass, J., and C. Filsfils, "Towards Lossless Video Transport (in submission to IEEE Internet Computing)", 2011. [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, September 2009. [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message Specification", RFC 5751, January 2010. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. Authors' Addresses Ali Begen Cisco 181 Bay Street Toronto, ON M5J 2T3 Canada Email: abegen@cisco.com Yiqun Cai Cisco 170 W. Tasman Dr. San Jose, CA 95134 USA Email: ycai@cisco.com Begen, et al. Expires September 13, 2011 [Page 7] Internet-Draft Temporal Interleaving Attribute in SDP March 2011 Heidi Ou Cisco 170 W. Tasman Dr. San Jose, CA 95134 USA Email: hou@cisco.com Begen, et al. Expires September 13, 2011 [Page 8]